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How often does fuel dumping from planes in flight actually occur?
There are a couple of questions about the emergency procedure of fuel dumping, used to reduce the weight of airplanes to be able to land.
This is certainly interesting, regarding environmental affects, safety aspects, and maybe some archaic fascination for huge fuel-air clouds.
How relevant these questions really are depends on how often fuel dumping is done.
But I don't know how often it is actually done, in incidents per year globally.
I understand that the procedure is used only in emergency cases, but not only in very few very extreme situations. It's about getting the weight down to be able to land safely, and the overweight is from fuel not yet used up on the flight.
So the procedure is needed whenever there is a need to urgently land, and there is not enough time to burn the fuel in flight.
That seems to mean that severe medical emergencies of individual passengers may be a reason? That happens much more often than drastic technical problems I assume, so it would be a strong factor.
Now, I'm interested in some rough total estimate about how often fuel dumping happens, and the main factors, like minimal emergency cases that can lead to a fuel dump.
I'd simplify the scope by considering only commercial aviation, ignoring military and general aviation - but I do not see that as important, use the data you have at hand.

Perhaps specify if you mean civilian or military aviation. Bare in mind that most military aviation records may be sealed (or non-existent)

you could search dump fuel on the avherald.com for a quick gander (not a full sample though)

@MatthewPeters good point, thanks!

@ratchetfreak Oh, that looks like not far away from at least the number part of the question. Aviation Herald search on "dump fuel"

@VolkerSiegel except it doesn't report all incidents (in part because the guy doesn't get all reports or the country would otherwise be misrepresented)

@TylerDurden Ah, ok; Are there statistics about how often dumping passengers does actually occur? ;)

These two reports cite that the US Air Force at one time jettisoned fuel nearly 1000 times per year. The second report also mentions that commercial airlines reported 485 instances of fuel jettison over a 5 year period. The commercial reports are only for maintenance related cases though, not including scheduling or weather reasons.
Both of these figures date from the 1970s. Military standards have been changed since then to reduce the frequency of it. The first paper assumed that in 1995, military fuel jettisoning was "infrequent".

In commercial aviation fuel is dumped rarely.  Only if the aircraft is taking off above max landing weight and an emergency takes place shortly after takeoff would a commercial aircraft be required to dump fuel.
Military cargo aircraft have max landing weights similar to their max takeoff weights, so they also rarely dump fuel.  Military tanker aircraft are probably the most likely to dump fuel as their max takeoff weight is well above their max landing weight.  In this case, two scenarios would drive dumped fuel - 1) An emergency condition that will require the aircraft to land prematurely within the first couple hours of flight 2) the loss of receiver aircraft driving a condition where it would be more efficient to dump fuel and land rather than fly until the fuel is low enough.  This probably occurs once a week.  I'd probably estimate that all of commercial aviation dumps about as much as the US tanker fleet, but that is just a wag.
Regarding the fuel clouds, the altitudes where fuel is intentionaly dumped are high enough so that the fuel quickly disperses and is not an environmental factor.  Furthermore, there are prescribed dump locations which are located away from populated areas.

OP knows the fuel dumping happens "rarely," and (I believe) was looking for some numbers. Do you have any specific numbers about how often fuel dumping happens?

You need to add an "and the aircraft is capable of it" — it might be ideally required to, but be unable to.

In my experience as an EC-121 crewman in the late 1970s (Lockheed Constellations) we dumped fuel fairly often (3 times on my own missions) due to the tendency of these older piston engine aircraft to blow out one of them on takeoff.  These aircraft carried a large fuel load as well as electronics and other equipment.

Whether or not dumped fuel is an environmental factor seems debatable.


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Is an afterburner louder than the same jet engine without it?
I would speculate that an afterburner increases the noise because it is nearer to the exhaust. But it certainly causes so many changes in the exhaust flow that it could be less loud as well. It may also depend on the shape of the nozzle.
That an afterburner increases the spacial volume of exhaust gases does not necessarily mean that the sound volume increases as well, because it strongly depends on the level of turbulence.
Does activating an afterburner make a jet engine louder? And why?

Keep in mind military jets with afterburners are already insanely loud.  They're not LEAP-X's.

This PDF indicates an increase by ~10 dB for an F-8K in afterburner versus the same aircraft in 100% dry thrust.
This PDF indicates smaller increases:

+5 dB for an F-15
+4 dB for F-22 and F-35

Worth noting that the decibel is a logarithmic measurement, and that human hearing has a more or less logarithmic response. So, an increase of 3dB indicates a sound of twice the intensity (ie. the actual energy in the sound), while an increase of 10dB will sound "twice as loud" to the human ear.

@anaximander yep - and also that the human ear's responsiveness varies with frequency.  So as per Michael Hall's answer, its possible for louder to merely sound "different" as the pitch/frequency changes.

@anaximander Yes, hearing is logarithmic. We can hear sounds over a large range of intensity. What is interesting is that we are talking about jet engines that are so loud that they are outside that range as experienced otherwise. I expect, somehow, that hearing two different engines from nearby can not differ in how loud they are because the human sense of hearing goes into saturation, to the maximal perceived loudness. Maybe that is when the ear get's mechanically destroyed. A difference can be always perceived from mechanical effects, of course.

It has been around 20 years since I've been on a carrier deck, but I recall that it wasn't as dramatic of an increase as you might think.  It may have gotten a little bit louder, but what I remember more is that the tone changed.  The sound was more "full" when the afterburner was engaged.  I realize this is a rather subjective answer.

That's not subjective, and interesting! I did not anticipate that it could be different with the same volume. It means it is louder at some frequencies, and quieter in others. So the volume difference depends on the method of measurement.

on a carrier deck, everyone wears a helmet which provides noise reduction - but this reduction is frequency-dependent. That will have influenced your experience.

@Hobbes Usually earplugs plus the helmet.  The combination provides about 40-50dB attenuation from 100-2000Hz, and about 60-65dB attenuation above about 2500Hz.  That certainly distorts the perception of the sound.  This paper studied the F-22 and found about a 5dB increase in sound pressure with reheat on.  I suspect the F-22 is probably quieter than older generation aircraft - certainly at airshows I've often noticed the afterburner being considerably louder than mil thrust - especially when facing the business end.

It's worth remembering that while the protection does change the experience, so would going deaf.

@J... Your comment could be an answer. It provides a clear answer (yes, by 5dB for the F22) with link to support it and for further reading.

@VolkerSiegel Nitpick: This is the textbook definition of subjective.

@JollyJoker I think subjective refers to a human subject, it means it depends on the observer. But it even depend on the method of measurement. And for each method of measurement, it is well defined and objective.

I must agree with both of the comments.  Yes, lighting the burner was louder.  Standing near a flight of F-16s when they lit the burners for takeoff, you noticed not just the noise level but also the change in character; deeper, fuller sound and you felt the vibrations through your boots.  Being inside a "hush house" with one was noisy but when the burner lit, the noise level was nausea-inducing.  Even with J's mentioned double hearing protection.

I would say definitely yes, because of all the extra energy added to the exhaust flow and it's obvious to anyone who attended enough military airshows.  Watch an F-16 depart with reheat on, then reduce thrust to military power (max thrust with reheat off) on the climb out, and it almost sounds like the engine flamed out.
The flow out the nozzle may be just over mach at military power, but will be well over Mach 2 with reheat on.  The nozzle changes shape with afterburner to manage all the extra energy and pressure, from a straight convergent duct to a convergent/divergent duct, like a rocket exhaust bell.
Although he doesn't cover the noise issue, this video explains why the nozzle has to change shape to control the mass flow through the engine because of all the heat energy added (math warning to those put in a catatonic state by arcane formulae).  The extra sound that results is a given.

I used to live near Farnborough - under the flight path in fact. I always got a good show and can definitely confirm that it's significantly louder.

To explain if the afterburner makes the engine louder, you must understand what the afterburner does. In the afterburner, the exhaust gases are re-heated by injecting fuel in the afterburner duct. The left oxygen is used to burn the fuel, which results in an increased exhaust gas flow. Note that the engine itself will not spool up faster: this is done by opening the exhaust nozzle; without opening the nozzle, the pressure would be too high and the fan would stall.
The extra gases leaving the engine produce a higher velocity jet stream; more mass and more velocity will yield more thrust, which is the purpose of afterburning fuel. If you look at jet noise modelling, you will find that the formula to calculate the jet noise includes the exhaust velocity (to the power of 8), so increasing the fuel flow and increasing the velocity will also increase the noise production.
The referenced model has been implemented in our gas turbine simulation program and verified against the noise measurements of a fighter aircraft to find that this model perfectly agrees with the measurements.

Nice first post! Welcome to Aviation.SE, I hope you stick around.

From an energy standpoint, the engine produces heat, thrust, and less significantly, sound. Ignore the afterburner for a second and just consider throttling up, whether a jet or your car. The engine gets louder. That's not a law of physics, that's just what happens. There's no theoretical reason why the extra waste energy can't go 101% into heat, and -1% into sound (think of noise-cancelling headphones) or into sound at frequencies inaudible to the human ear. But practical combustion engines get louder (both overall and to the human ear) as they burn fuel faster.
You would be surprised if throttling up made your engine quieter.
The same goes for increasing fuel burn via afterburner, only more so. For one thing the afterburner is inefficient, so there is a higher proportion of waste energy to dissipate. For another the afterburner noise happens later and is less controllable, even if there was any desire to do so.

An ICE may not be a good comparison since much of the noise is caused by mechanical movements of the engine (pistons, camshafts, lifters, belts, etc.).  However, the reason more energy => more sound for a jet is entropy.  A cloud of combusting gases cannot be expected to form a noise-cancelling system, nor is it reasonable to expect that such a system is feasible.  The sound volume is directly related to the velocity of the exhaust stream as well as vibrations induced in the mechanical parts of the engine (compressors, turbines, etc.).

If you are asking if the engine is louder, no it is not. The afterburner and the diversion of the exhaust is what makes it louder. Just like in a car motor running straight pipe to gain horsepower. You can take the same motor and put an exhaust system on it and it will give that motor a different tone.

Isn't an afterburner part of the engine? It's just a second fuel injection. The nozzle is after it, and a relevant part of the engine.

Hi and welcome to Aviation.SE! Your exhaust pipe analogy is not really applicable to an afterburner because exhaust pipes are a net energy sink while afterburners add energy to the system by working as a rocket engine of sorts.

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Do afterburners use excessive amounts of fuel?
The purpose of an afterburner is to provide additional thrust, and it is obvious that more fuel is needed for that.
But that is to be expected independent of an afterburner. That more thrust needs more than a proportional increase of fuel may be the case because the thrust increase needed per speed difference is not linear¹.
The reason to build afterburners may be that stronger jet engines can not be build with the same mass or volume. Or that a stronger jet engine is not useful in standard use, for example because the fuselage would overheat.
Doubling the speed increases the fuel usage by more than double I would expect, purely based on aerodynamics, independent of the engine.
Is the fuel usage for increasing speed greater with an afterburner  than with a stronger jet engine? How much? Why?

¹ For spaceflight, that is true according to special relativity.

The reason to use afterburner than other alternatives is alternatives don't exist. You want a fighter to run mach 2 without using afterburner? Are you willing to wait for 3 decades for that?

@user3528438 But an engine could be larger, and even a solid fuel booster rocket would be an alternative, and has actually been used, I think.

@user3528438, er, Concorde flew Mach 2 without afterburner 3 decades ago. Volker is right, the engine could 'simply' be larger. The limiting factor is the turbine temperature, which doesn't allow the mixture to be rich enough and 'simply' pump in more fuel without increasing the air flow (i.e. making the engine larger).

Define "excessive". Excessive assumes the same effect can be attained at a lesser cost, or the effect is unnecessary. Neither is the case with afterburning engines.

@Zeus Concorde did have afterburners and they were required for takeoff and pushing through the Mach barrier, after which they were turned off for supersonic cruise.

Yes the specific fuel consumption of the afterburner, lbs of fuel used per lb of thrust, is much higher than the core engine.  This is because the fuel is being added to a part of the engine where the air is less compressed, so the energy conversion is a lot less efficient. The bright orange flame coming out the tail pipe when in reheat is pretty much all that un-oxidized carbon fluorescing - wasted energy. See this article.
Fighters use reheat because all that extra power is available with minimal extra weight (the weight of the burner and additional fuel), but they can only exploit that power for short periods if they want to have decent range or endurance, so they are generally used for dashing somewhere, or to assist with maneuvering, or taking off with a heavy load.

The carbon present in the exhaust convinces me that an afterburner is less efficient. Using it on takeoff means it is used subsonic - that makes the whole topic more interesting. I'll remove the assumption of supersonic flight.

@Guy Inchbald  I rejected your edits because some of the changes are stylistic plus there is so much extra material in there you should really just create your own post.

If you look at it in terms of thrust vs fuel flow, then yes, they're very inefficient.
However, if you just look at the amount of fuel burnt to get an interceptor from the runway to 30,000ft, then they can be more efficient. Without afterburners the same climb would take significantly longer and could use more fuel.
Without afterburners, you'd need much larger, heavier engines to reach Mach 2 and it might not even be possible to get to the same height and speed in the same time, which after all, is the point of an interceptor.
Think of it this way: if minimum fuel was the only criteria, we'd send the pilot by train.

Yes they do use a lot of extra fuel, but the amount is depending on the operating conditions (Mach flight speed and altitude)!
Comparing MIL (military) power setting (maximum power without reheat) to MAX power setting (engine will be in MIL power, but the reheat will be scheduled and the exhaust nozzle opened) you can see that it is not uncommon to have 3 to 6 times as more fuel flow depending on Mach and altitude and the gas turbine.
Note that burning fuel at a low pressure is not very effective in terms of efficiency, but in power output it is very large. Again, depending on the operating conditions it is not uncommon to double the amount of thrust.
The questions you ask about using a bigger engine is not easy to answer, increasing the engine (for a design, you cannot increase the engine simply for an existing airframe) would also increase the frontal area and as such more drag. Such questions could be answered with a gas turbine simulation program in combination or coupled with an aircraft flight model.

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Is this how ailerons are actuated?
I was wondering how ailerons work on fighter jets. I came across this after hours of research.

Is that how fighter jet ailerons work? Is their a better picture or image that would be better. If there is please post it to help me understand. I've researched for so long on this subject with no avail except this picture that helped me understand it. Thank so much!

Can you tell what you don't understand? That might help to find something that helps with the points you didn't understand yet.

I don't understand how the linear actuator causes the aileron to move. I found this picture but I know its a bit too simple and its not the full process. Im looking for a picture that would explain how this works.

I edited the title to be more precise. As I understand, you are interesting in how they are put in movement, not the other aspects of how it works (e.g. aerodynamics). Feel free to edit again if I misunderstand what you mean.

Ok thank you. Im sorry my titles are not clear enough. Im new on the aviation stack exchange

Your question posts two different pictures of different mechanisms and then says "Is that how fighter jet ailerons work?".   I think the question could be improved to be more clear as to what you want to know.

In the lower picture that accompanies the graphic in your link, focus on the elongated figure eight shaped piece.  The lower portion is attached to a piston extending from the actuator, and is free to pivot about the attaching point.
The upper portion of this link is fixed to the aileron and the entire part acts as a lever arm.  So, when the dark gray piston of the actuator moves left and right, the figure eight lever pivots clockwise or counter clockwise centered on the middle of the upper circle.  Since this part of the link is attached to the aileron, it also moves.
The graphic isn’t great, but try to visualize which parts move from my description and let me know if you are still confused.
You typically won't see the actual control horn on full sized aircraft because it will either be covered be a fairing to streamline it, or it will be contained within the thickness of the wing structure.
For example, in small RC models it is common to have an external horn like this:

However, you will generally NOT see a large external actuator like this on a full sized plane:

There simply isn't a need for such a large mechanism on most airplanes, and it would come with a large drag penalty.  If extra leverage is needed and the mechanism protrudes beyond the thickness of the wing it will be covered by a fairing like this:

Instead, most designers will try to keep actuators contained within the wing, as in the photos below:

Hi im still confused about why you dont see the control horn on the aielron on planes. Sorry I replied to this comment very late

@Luke Justin, the control horn is internal, just like in the diagrams you included with the question.  Full sized aircraft do not have this part on the outside like RC planes you may have seen.

The figure 8 is the horn...

I know but how do they cover it up on the aircraft? Is the fairing attached to a hinge on the control horn?

It's just contained within the thickness of the wing structure, or there may be a bump to cover it. I don't know how to explain it beyond that. Your diagram is a generic example, aircraft differ somewhat. My best recommendation would be to go look at a real airplane. I don't think it needs to have hydraulic controls to make the point, find a local flight school or airplane museum and ask there.

@Luke Justin, see additional photos in my answer and let me know it that helps clear anything up.

Thanks the pictures helped so much. However, how do they contatin the mechniasm in the wing. Is their a picture of the whole mechnisms in the wing not just close up?

The photos are General Aviation aircraft and homebuilts, not fighters as you are asking about.  So, they have manually actuated controls using pushrods and cables.  But, try to visualize a hydraulic cylinder in there instead of a pushrod and I think you will get the picture.  I just found these by Googling keywords like "aileron actuator" etc.  Dig a little, use your imagination...  it is a pretty simple lever arrangement, I don't think you will get a better answer than what I already have given you.

Sorry if Im annyoing by keep asking you questions but this aileron actuator question is one of those I just cant go to sleep not fully understanding it. I understand all the components  involved. Ive researched diagrams of the f22&35 and I can even see the actuaors. I just dont really understand how it is covered up by the bulge/fairing yes still works. How is it possible for the fairing to be connected to the wing and the aileron even though they both move? Also in plane diagrams it seems the actuator is in the middle of the aileron not the side. That confused me (research f22 cutway diagram)

I'm just not sure what your hang up in understanding is.  It isn't an F-22 or F-35, but look at the third photo in my answer.  Half the fairing is attached to the wing, and half to the aileron.  One of these pieces can slide inside the other when it moves.  This was described by someone on your other post who compared it to the way an elbow joint on a suit of armor moves.  And in your other post, you can clearly see this same type of seam on the photo you posted of the F-22.  There are two separate parts that are rigged to work together.

I'm just not sure what more I can say.  If words and photos are not enough I would recommend you find a local mentor who can help demonstrate some of these mechanical concepts to you.

I am young and really want to be an aerospace engineer...but have bassicly no mentorhsip and nothing to guide me. I really dont have any kind of mentor around. (The thing I am still consufed about the aielron is like a video of it moving from the underside of the plane so I can see how the fairing moves and stuff. Also was the third and fourth picture you added to the answer from a video?)

I wish I could help you more Luke, I have just run out of ideas.  I just pulled the photos from Google images.  Do you live anywhere near Seattle by chance?

Any there any nearby flight schools?  Does your school have a STEM program?  Are there any Civil Air Patrol squadrons in your area?  These are all good ways to find a mentor who can guide you.

I accutly was going to join a Civil Air Patorl sqaudron nearby but because of covid I cant. I thought they only teach you how to fly. The teach you also about engineering?

Not straight engineering per se, but you can learn a lot about airplanes.  Squadrons can vary somewhat depending on members, and their expertise and interests.  I would encourage you to look into it when you have a chance.  Check out a couple squadrons if there is a choice.  Good luck!

Does your school have a robotics program?  Also, (not sure your age...) consider something like an Erector set.  I picked up a lot of practical knowledge and insight of basic mechanical functions playing around with mine as a kid.

My school isnt really big about engineering or that. I am in the robotics club but its Lego Mindstorm which is not that high level. If I do to college Im defiantly going to major in Aerospace Engineering and try to get an internship. Ive been looking for ways to enhance my knoweldge about the subject. I'm going to get into Civil Air patrol (when the pandemic ends) and I'm looking into a lot of books. Also I think there is a slight chance ill be allowed flight lessons soon. I just fear I wont picked be picked for a job/interneship because of me not knowing a lot about engineering.


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Why did the CL-400 Suntan have engines on the ends of its wings?
I've been reading more about the development of the A-12, which in turn referenced the CL-400 Suntan. I noticed that the engines are located at the end of the wing, rather than integrated with the fuselage or on the midpoint, which is not something I've seen (or at least noticed) on any other aircraft (the closest thing I'm aware of is tip jets on helicopters). What is the design rationale behind locating engines on the end of the wing, and indeed for other locations?

See engine locations in general, and locations far from the fuselage

The asymmetric thrust of single-engine operation must have been considered and deemed manageable... or was it deemed to be of low enough probability for a military aircraft that it would be cause for bailout?

The Suntan project needed all fuselage space to hold three tanks for liquid hydrogen, so the engines had to be placed somewhere else. Placing them near the fuselage would put them in the range of the fuselage's shock waves. Putting them out on the wing would help with wing bending relief and ensure a clean intake flow. Once they are so far out, you can as well put them on the wingtips, so that they do not cause a pitch-up moment. On the SR-71, the engines were also placed outside the fuselage and into the wing's plane, much for the same reasons.
Keeping the intake flow uniform is paramount for the undisturbed operation of supersonic intakes, and I assume that Kelly Johnson wanted to make sure that the engines would not suffer an unstart when flying reconnaissance missions over hostile territory. With the little experience in supersonic flight in 1955 it was prudent to avoid built-in pitching moments - after all, the supersonic L/D likely was in the single digits, so an out-of-plane engine placement would had produced more moment than on subsonic aircraft.
Hydrogen was selected to achieve the highest possible flight altitude, so the aircraft would be safe from surface-to-air missiles for as long as possible. I initially thought that the wingtip location would enable to cool the hot wing structure by heating up the hydrogen on its way to the engine, but heating was planned to be done with bleed air in a special heat exchanger. Quoting www.history.NASA.gov:

The CL-400 design divided the hydrogen tankage into three sections;
  the forward tank had a capacity of 67 000 liters; aft, 54 000; and
  center (sump), 15 000. The two main tanks were kept at 2.3 atmospheres
  pressure and the sump tank slightly lower for fuel transfer. In the
  sump was a booster pump, built by Pesco Products, that supplied liquid
  hydrogen to the engines at a pressure of 4.4 atmospheres. The engines
  were mounted at the wing tips, which meant that the liquid hydrogen
  had to pass through a hot wing with surface temperatures up to 436 K.
  The design provided a vacuum-jacketed, insulated line for this
  purpose.

Regarding the perceived danger of using hydrogen, www.history.NASA.gov says:

Tests were devised in which tanks containing liquid hydrogen under
  pressure were ruptured. In many cases, the hydrogen quickly escaped
  without ignition. The experimenters then provided a rocket squib (a
  small powder charge) to ignite the escaping, hydrogen. The resulting
  fireball quickly dissipated because of the rapid flame speed of
  hydrogen and its low density. Containers of hydrogen and gasoline were
  placed side by side and ruptured. When the hydrogen can was ruptured
  and ignited, the flame quickly dissipated -, but when the same thing
  was done with gasoline, the gasoline and flame stayed near the
  container and did much more damage. The gasoline fire was an order of
  magnitude more severe than the hydrogen fire. The experimenters tried
  to induce hydrogen to explode, with limited success. In 61 attempts,
  only two explosions occurred and in both, they had to mix oxygen with
  the hydrogen. Their largest explosion was produced by mixing a half
  liter of liquid oxygen with a similar volume of liquid hydrogen.
  Johnson and Rich were convinced that, with proper care, liquid
  hydrogen could be handled quite safely and was a practical fuel-a
  conclusion that was amply verified by the space program in the 1960s.
  At the time, however, Johnson and Rich filmed their fire and explosion
  experiments to convince doubters.

When work on Suntan started, liquid hydrogen was a laboratory curiosity. Preparing the infrastructure needed for operating the CL-400, the Suntan project led to the building of large-scale liquid hydrogen plants. Their availability paved the way for the cryogenic rockets of the Apollo program!
Interestingly, a similar engine location was selected by the Russian design bureaus Tsybin for their NM-1 and Myasishchyev for their M-50 supersonic bomber in the mid-50s. It was started after news of the US Weapon System 110 (which later led to the XB-70) reached Russia and was similarly cancelled after two prototypes had been built and only one aircraft had flown.

M-50 during display in 1961 at Tushino airshow (picture source). Note the similarity of the Mig-21 and M-50 planform - both originated from the same work done at TsAGI.
Placing the outer engines below the wing would had caused ground contact on rotation. Speaking of rotation: The M-50 had two central gears and the bomb bay between them, and the main gear had to be placed so far aft that the M-50 could not be rotated the usual way with the elevator. So the engineers devised what they called the "galloping bicycle". When the aircraft reached 300 km/h, the forward gear rapidly extended to rotate it to 10°. Placing the outer engines B-58-like below the wing would had required an even longer gear.

The position of the engines on wing is determined by a number of factors:

Aerodynamics: The flow at engine intake should be as undisturbed as possible. The drag should be kept as low as possible.
Safety: Any uncontained engine failure should not affect other components (like fuselage, wing or other engines).
Control: In case of multi engined aircraft, asymmetric thrust due to the failure of one engine should not produce uncontrollable yawing moment.
Comfort: In case of civil aircraft, the cabin noise due to engine should be minimal.
Structural: The location of engines far from the center-line gives beneficial wing bending relief in flight.
Fuel capacity: the location of engines in pods outside the wing frees up space for fuel in the wing.
Maintainability: The engines should be easily accessible for maintenance and repair crew.

The CL-400 had its engines in the wingtips, that freed up the fuselage to carry the fuel. A similar arrangement was found in the Myasishchev M-50

Image from testpilot.ru
Both were designed to be high speed, long range aircraft, with neither fulfilling their requirements.
Another aircraft with wingtip engines was the French Trident, which was expected to be a rocket powered interceptor.

"SO.9000 Trident" by Deep silence (Mikaël Restoux) - Own work (Bourget museum, in France). Licensed under CC BY-SA 2.5 via Commons.
Also, some P-51s were fitted with wingtip rocket ramjets for increasing their speed.

Image from jimbrooks.org

The trident is a cool-looking airplane! Is it the angle or are the wings not swept at all?

@TomMcW it indeed has straight wings, essentially just slabs of metal. Remember this was built in France just after the war by engineers who had no access to German, US, and British research into high subsonic and supersonic aerodynamics. They were effectively trying to build a supersonic aircraft using 1930s aerodynamics knowledge.

What on earth is a rocket ramjet?

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Will this diagnosis from my cardiologist prevent me from getting a Class 1 JAA medical?
In 3 days I will have my Class 1 JAA medical test for the first time. However I said let's do a heart checkup before I go there and when I did this suddenly my cardiologist wrote that I have:

Anterior mitral leaflet is slightly redundant and shows mild systolic prolapse. Trivial mitral regurgitation present.

He did for me a TMT and my performance was 97% as I'm 23 years old my heart rate increased to 195 bpm.
He told me this will not affect your pilot studies and nothing to worry about because it is normal and if you want to check it again, check it after 4 years, however no need to check it again.
Now I'm worried, will they stop me if they found out about this or what will happen?

I have no idea what the heart issues are but let me tell you that nobody is ever 100% free of some sort of medical condition that isn't quite the norm. As long as you won't pass out at the controls you'll probably be fine. Make sure you tell the JAA because hiding it will be a bad look and could be grounds for cancellation. Let us know how the medical goes.

sure, i hide it or not whenever the doctor put his stethoscope on my chest he will know about it.

i passed my medical exam and it was good, this issue wasn't a big problem at all even its not a problem.

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Why is carburetor heat use discouraged on the ground?
I've been reading my private pilot books for when I start in February and Carb Heat has me stuck in a rut. I feel like I need to have a very solid understanding of this being that I live in a very humid area. The book says do not use carb heat on the ground and on taxi because it will draw unfiltered air into the engine(air from exhaust)... But what is the difference between using it in the air vs on the ground and isn't the risk of icing just as equal in the air as on the ground?

Point 2 here does address this a bit

If you feel that you would need carb heat sitting on the ground, I'd recommend taxing back and waiting for conditions to improve. If you are set on going, usually doing a run-up at the runway before take-off will tell you if you have carb ice or not.
The other answer gave good reasons, sucking in some FOD (foreign object debris), but there are some other things you would want to consider...
Forgetting to push the carb heat back in before takeoff
 - Especially important when taking off from short fields, you want all the power your engine has to offer, as carb heat robs your engine of some power. If you have carb ice, applying carb heat will cause your engine to make even less power (hot air is less dense than cold air). 3/4 of the way down a 1200 foot runway is a bad time to realize the carb heat is still on, because it probably isn't on your takeoff checklist.
Carb heat is not very effective on a cold engine
 - This is a real problem when you are at idle or especially gliding, the airflow over the engine components and the exhaust just doesn't create enough heat to melt the ice in the carb (at least not very quickly). This is why you may be instructed to "clear" the engine periodically during low power operations. This involves adding power and then carb heat to help melt any ice.
That all being said, its not so much a rule as a recommendation. You'll probably find that during your flight training you'll end up leaving the carb heat on while on the ground for short periods. This happens a lot during landing operations when you are instructed to have carb heat on (my instructor taught me mid-field downwind, "Seat Belts, Gear, Fuel Selector, Carb Heat, Mixture, Prop, Power"). You'll end up leaving it on until you've cleared the runway (or set up for a touch-and-go) and are running your "after landing" checklists.

Several possible reasons.  While taxiing an engine failure is not as critical.  While in flight an aircraft is much less likely to ingest dirt, rocks, twigs, grass etc.  Finally, while at flying speed, the exhaust gases are carried "behind" the aircraft, while at slow taxi speed, there is less airflow to do that.

The Owner's Operation Handbook for the Luscombe recommends carb heat be ON during landing AND takeoff. In the models where the fuel tank was in the fuselage, apparently there wasn't enough fuel head to get the fuel to the carb under full power climb (too steep an angle), but the handbook explicitly references icing as the reason for carb heat during takeoff.


text:
What should I know before getting the KAMRA laser eye surgery procedure as a pilot?
I was recently looking into the KAMRA procedure to fix my reading problem. Then I came across some posts that discourage it as it causes one to see halos in night so particularly bad for pilots. I was wondering if anyone else here has done that that what was his or her experience about it? What are the regulations on this as well?

related: http://aviation.stackexchange.com/q/16587/1467

Welcome to aviation.SE! Please always mention which regulations you're asking about: FAA, EASA or something else.

I had Kamra surgery about 4 years ago. In the beginning, there were some issues with halos and blurred night vision. After a few months, those issues disappeared. I now have excellent vision and only use reading glasses in low light conditions. It is so refreshing to read an email on my phone without having to find my glasses!

I'm not clear if you are asking about LASIK or KAMRA, the former is accepted by the FAA, while there is no explicit mention of the latter procedure.
The procedure site itself mentions halos as one of the side effects of the procedure:

The KAMRA inlay procedure may cause blurred vision, difficulties with contrast sensitivity, problems with night vision, double vision, ghost images, glare, halos, and color disturbances.

In general, people with such adverse effects and complications are not allowed to serve as airmen:

The FAA expects that airmen will not resume airman duties until ... there are no significant adverse effects or complications (such as halos, rings, haze, impaired night vision and glare), ...  and reviewed by an Examiner or AMCD.

The medical certificate for a person who had undergone such procedures is contingent upon the absense of any side effects affecting vision:

An applicant treated with a refractive procedure may be issued a medical certificate by the Examiner if ... the applicant does not suffer sequela such as; glare intolerance, halos, rings, impaired night vision, or any other complications

It would be better if you consult a doctor to find out if the procedure is suitable for you and possibility of side effects.

Another problem can be pressure that can have effect on the eye. In the event of rapid decompression it's possible to lose vision. There a lot different opinions about this. Probably also depends on the particular case. If you watched movie Into Thin Air: Death on Everest about 1996 disaster one of the climbers got blind due to lasik.

I was about to add the Everest event as a comment and then saw your answer. The book / written account is good as it contains the sort of detail that is liable to get missed in a movie. Title was "Into thin air" AFAIR.

@RussellMcMahon, you seem to remember correctly (I'll just edit wikipedia links into the answer).


text:
Why do you need to subtract when using a climb/descent performance chart for an altitude other than sea level?
If you look at this chart you see we subtract 3 minus 1, 9 minus 2, and 30 minus 4 in the example calculation. My question is, why do we subtract these numbers? Do we subtract the same numbers each time? Nowhere on the performance chart does it give any explanation!

There is something wrong about this chart.  The very top states to descend at 500 FPM.  If you descended to a sea level airport from 5500' it should take 11 mins.  The example shows 9 mins or 611' FPM.  Since the pilot is trying to maintain 500 FPM it would negate any atmospheric differences from standard.

wbeard52 raises a good question. Can someone comment on this? Why does this chart have this discrepancy?

Most likely it is calculating a descent to pattern altitude, not all the way down.

Somewhere in the POH it should tell you why this is.  Lnafziger may be correct.

I just downloaded the POH.   The chart shows 11 minutes while the example indicates 9 minutes.  They (Piper) read their own chart incorrectly.

If you look closely at the example, it's describing a situation where you're cruising at 5500 feet, and landing at an airport with a "pressure altitude" (elevation) of 680 feet. The chart, however, is indexed to zero-altitude. You can't just reduce your cruise altitude by the elevation of the airport, because performance varies with altitude (indicated by the curvature of the arcs for fuel, time, and distance).
To find what you'd need to descend to the airport, you must run the numbers twice - once for descending to sea level from cruise (3 gallons, 9 minutes, 30 NM), and once for descending from the airport to sea level (1 gallon, 2 minutes, 4 NM). Note the two sets of dashed arrows on the chart, providing the two example calculations. You then subtract the numbers for the airport from the numbers for the cruise altitude, as you would hopefully not descend below the altitude of the airport!


text:
Can weight shift control aircraft be used commercially?
Can a WSC aircraft registered SLSA be used commercially i.e., local tours for hire?
FAA regulations do not seem to address a commercial rating for WSC.

I know nothing about WSC but what would happen if passenger shift his weight in undesirable position?

I don't know much about LSAs, but the regulations say that LSAs with a special airworthiness certificate may not be used in commercial operations (with two exceptions).
This FAA document says that a weight-shift-control LSA will have a special airworthiness certificate:

A special airworthiness certificate in the light-sport category is
  issued to an aircraft that meets the definition of light-sport
  aircraft (LSA), is manufactured to the applicable consensus standards,
  and is one of the following five classes of the LSA category:
  airplanes, gliders, powered parachutes, weight-shift-control aircraft
  (commonly called trikes), and lighter-than-air aircraft (balloons and
  airships).

And 14 CFR 91.327 says:

(a) No person may operate an aircraft that has a special airworthiness
  certificate in the light-sport category for compensation or hire
  except—
(1) To tow a glider or an unpowered ultralight vehicle in accordance
  with §91.309 of this chapter; or
(2) To conduct flight training.

I am by no means familiar with all LSAs, but the thought of using a powered parachute, WSC/trike or balloon to tow another... anything... is somewhere between amusing and terrifying!

All commercial operations require a pilot who holds a commercial or ATP certificate with appropriate ratings at a commercial level or higher.
There is no provision in the FARs to give pilots a commercial WSC rating.


text:
What Blackbird variant is the one at the Kalamazoo Air Zoo?
Which one is sitting at the Air Zoo (Kalamazoo Aviation History Museum)? What variant is it?

Are you comparing the M-21 (an A-12 variant) in Seattle with the SR-71B in Michigan?

The Air Zoo refers to it as an SR-71B.  Their image of it shows it in NASA livery as NASA 831. This was originally USAF serial number 61-7956 which was one of two SR-71's built as trainers. 61-7957 was the other and it was destroyed in a crash in 1968.  They were both built as SR-71B's, not A-12's or YF-12's.
Number 956 was transferred to NASA in 1990 when the AF retired the SR-71's the first time. NASA labeled it as #831.
There is only one other dual-control trainer and it is an SR-71C, serial number 61-7981 which replaced the destroyed #956.  It was made from parts of the static test model SR-71 and the aft section of YF-12A #06934.
More info at Habu.org.

I'm confused by your comment that there is only one other "two-seater".  In The Blackbird Diaries almost every single story refers to the "back seat" and a second crew member.    I believe that all the Blackbirds carried two crew members, but only the 71B and 71C could be piloted by the second crew, is that correct?

@abelenky You're correct. A limited number of two-seat, dual-control trainers were built, which is what Gerry is referring to.

@abelenky Your assumption is correct. I also found an image at the Air Zoo and confirmed the a/c number.  I've updated the answer.

@egid Thanks for the clarification.  I've edited the answer to reduce ambiguity.


text:
Why does the A-320 allow 1.3 degrees more left rudder trim than right?
On the a320, can someone explain why this is:

AMM 27-22-00 PB 001
  NOTE:The maximum admissible rudder trim limits
  indicated on the control panel when the aircraft is stabilized in
  heading with the AP engaged are RH 1 DEG and LH 2.3 DEG.

Why is there a 1.3 difference in deg between LH & RH?

Both engines turn the same way, and the bypass fans exert torque in order to accelerate the air passing through them. The torque needs to be trimmed out using aileron & rudder trim.

This is really interesting. It seems difficult for the pilot. Why don't the engines turn in opposite directions?

@BrianGordon: that would require two mostly different engines. Twice as much spare engines, higher production costs, and so on. Though, many propeller driven aircraft, where the torque plays a bigger role, have counter-rotating engines/propellers.

Also, it's easier to reverse the direction of a turboprop where you've already got a gearbox before the propeller. Turbofans generally have the fan on the same shaft as the low-pressure compressor and turbine, so you would need to rebuild half the core to change direction.

@BrianGordon it's not really a problem for the pilot when the designers have compensated for it, for example, by allowing more left rudder trim than right.


text:
Are there different symbols or graphics to identify different types of GA fuels?
Are there different symbols to identify the different types of fuels used for general aviation aircraft?

What do you mean by symbols in this context?

Specific graphyc symbols like letters numbers or something else, to designate each different type...

As Walker notes in his answer AvGas is typically noted by color when talking about telling it apart. In terms of aircraft markings for fuel this is governed by FAA FAR 23.1557 Miscellaneous markings and placards. and some more notes in this AC,

(c)Fuel, oil, and coolant filler openings. The following apply:
(1) Fuel filler openings must be marked at or near the filler cover with-

  (i) For reciprocating engine-powered airplanes -

    (A) The word “Avgas”; and

    (B) The minimum fuel grade.

These are fairly simple regulations to comply with so there is a wide variety of markings available, but the end results tends to be a decal looking something like this:

(source)
Above ground storage tanks will also have to comply with local state regulations on petroleum storage, here are the New Hampshire regulations as an example. Generally this will require an NFPA style decal but pilots dont really use those to identify anything. The typical signage for 100LL is a red back, white fount, all caps AVGAS 100LL this is common on tanks,

and trucks alike,
(source)

(source)

Its also important that you as the pilot are present for fueling both to verify type and quantity. If there is any doubt about what is in a truck or at a pump some should be pumped into a canister and verified by color before fueling an aircraft.

There is also a standard set of symbols/signage for tanker trucks to use - not sure if this only applies on public road or if an airport tank truck like pictured would need to have it as well.  http://dtectsystems.blogspot.com/2013/04/normal-0-false-false-false-en-us-x-none.html

My Cessna only requires this wording to be in place "Aft of the fuel tank":  "Service this airplane with 91 / 96 minimum or 100 / 130 grade aviation gasoline.  Total capacity 25 gal. Capacity to line of holes inside filler neck 22.0."

There is 87 Mogas, 100 Low Lead (100LL), and 130.
100LL is pretty common for the 4 and 6 cylinder general aviation aircraft (single and 2, 4, 6 seaters with one and two engines).
87 and 130 are getting less and less common. I don't think I've ever seen 130, altho my plane is placarded to use 100LL or 130.
Larger planes than that and you start seeing Jet A fuel used in single engine and twin turboprops, turbine, and turbofan equipped planes.
For example, in western NY, you can see prices in the Buffalo area for Jet A, 100LL, and Mogas:  http://www.airnav.com/fuel/local.html enter BUF or KBUF.  You can try other areas also, such as LAX (Los Angeles), FTW (Fort Worth), JFK, STL (St Louis).

I don't think the OP is asking what the different types of fuels are, they seem to be asking if those fuels have an associated symbol.

Only the name, as far as I know.

Thank you anyway

Aviation Fuels are dyed different colors.

Jet A = Straw or Clear
82 Un-Leaded = Purple
100 Low Lead = Blue
100/130 = Green

When there were more grades containing lead there was Red and Orange.  Purple was 115/145 used in high power and military applications.

What colour is Jet B dyed?


text:
How can I rebuild my missing logbook after 20 years of not flying?
I took flying lessons when I was a senior in H.S. in Illinois.  I got through solo and all of my x-countries (even the long one).  I was about a month away from finishing when we moved to Colorado and I started engineering school.  I intended to continue flying but school became the priority.  I lugged my log book and text books around for years (I can remember seeing my log book only 4 years ago).  I am about to finish what I started and go back and start the process again.  Now of course I cannot find my log book (I have turned my house upside down) :(
I want to state (because I know someone will make the point) that I am not looking for a short cut and I fully intend to make sure I get great training (its been 20 years) and plan on working my way through the requirements for a second time. I will defer to my instructor on what I need to learn and practice. I remember I had about 80 hours and I would like to get credit for them (if only to show the new school that I'm not starting from ground zero) as well as I plan on getting my instrument as soon as I can and the hours would help.
The flight school is no longer in business.  I remember the first name of my instructor (and have the first solo picture).  I thought I could contact him if I could find his last name and search some sort of data base?  I have searched the business records of the state and found a business record that for the old flight school that lists the owner.  I thought I would start there and see if I get lucky. If I can find the instructor's name I think there is a good chance he'll remember me and could provide documentation that would allow me to start a new log book with credit for my existing hours.
I found a local news paper article from the time period that mentions another flight instructor that worked there (AmCorp out of Lansing, Illinois in 1995) at the same time.  Is there a way to look them up in some sort of pilot data base to contact them and see if they remember my instructor's last name?
I remember filing my flight plans (I assume there is no record of that with the FAA because it's so long ago)?
Hopefully you get the idea of my quesition and hope you guys can give me any ideas on resources that I don't know of that may help me out.

You could try the Airmen Inquiry Database to find the instructor. https://amsrvs.registry.faa.gov/airmeninquiry/ However, after 20 years, you should probably just let it go and start with a new logbook. So much has changed that you are basically starting over.

Related: How does a pilot replace their logbook if it has been lost?

If it has been 20 years, you will probably need the minimum solo time to get ready for a check ride.  Assume little is lost.  Part 91 or 141 school?

You will need to take the Knowledge Exam again as well. And get a medical.    https://www.faa.gov/uas/getting_started/part_107/remote_pilot_cert/

You will probably not be able to recover any solo flight time you have completed to this point, but contact your previous flight instructors in Illinois.  They should have logged the training time they did with you on dual instruction, which will allow you to recover that flying time this way.
If you don’t have contact information on this instructor, you may be able to search them out, either on the FAA’s website or third party flight instructor directories like this one.
http://www.iflightplanner.com/FlightInstructors/
Good luck

We’ll i found myself in the airman database at least (just medical certs).  Thanks for that resource (now I just have to find his last name).  I’m part 91 school (I own a business so this is for that and recreation).  I signed up for an online written testprep and will take it before I go back to the new school.  I figure if I can get a letter verifying my past training I can count the hours?  My thought is that if my skills end up not starting at zero I will be glad I have the hours to be able to move forward towards instrument rating sooner than if I have to build them up again?

Well in order to apply for private pilot certificate, you will need at least 20 hours of dual instruction time. If you cannot locate that old  logbook, you will have to make that time up with a new instructor.   Then again having not flown for 20 years now, you may have to spend that much time training in order to be proficient for the practical test.

This situation periodically comes up.  You did not give a good indication of how much flight time you had, but here is my generalized take.
Start anew.  Your prior experience will speed your training.  At least in my neck of the woods, most people who are 40 yo old are taking 60 to 65 hours to get their private accomplished.  Even if your previous flight time was 35 hours, you will likely require 30 to 40 hours to get preped for the private checkride.
If you end up finding yourself ready after 25 hours, which I doubt will happen, you can fly several longer cross country solo trips, or get some additional dual to enhance your attitude instrument flying and navigation skills.
The only students I have seen who are ready for their checkride before the FAA minimum hours are reached are young pilots, especially female ones.  40 years ago it was different, and there were students who were ready after 30 or even 25 hours if they came from a background with aviation (like family members who flew).
Therefore, it is rather unlikely that having those previous records will save you money on your training.  I would focus on starting, and making good headway. If it appears that you are progressing very rapidly, then I would suggest that you get an appointment with an FAA FSDO Operations Inspector. With any records, and perhaps even with an affidavit (assuming you clearly recall) you may get them to consent to a reconstructed log.
Focus on the work ahead of you and do well. Remember that there is no restriction on when you can solo, so if you are advancing quickly, you will get some early indications, and can plan accordingly.

"students who were ready after 30 or even 25 years" - I assume you mean "hours" there, not years?

Uh, yes. I will edit. Thanks.  At least someone reads what I write. Thanks!


text:
Why is laser illumation of a cockpit an emergency?
Another answer pointed out that laser illumination of a cockpit may be considered an emergency, and that pilots may take evasive action when under laser illumination.
Why is laser illumination considered an emergency?
Have any documented instances of laser illumination resulted in injury to or loss of crew, passengers, or plane?

@AbraCadaver You might be joking, but laser guided munitions rely on lasers outside the visible spectrum, to avoid warning the enemy primarily.  They won't be visible to the pilot of the aircraft.

OK, maybe laser "sighted" ;-)  I have plenty of weapons with this feature.

For further perusal: http://www.technologyreview.com/view/420214/the-danger-of-green-laser-pointers/

Let me posit a hypothetical game ("Don't Try This at... well Anywhere").
It's simple - there are just 3 rules:

Give your friend a nice laser pointer and have them stand at the end of a road
  A half-mile or so should be plenty.
Get in your car at the other end of the road and drive toward your friend.
Your friend's goal is to shine the laser in your eyes. Your goal is simple: try not to crash.

Clearly this is not a very safe game.
It should be clear that playing the same game with aircraft is substantially less safe. Someone attempting to "play" without your consent certainly rises to the definition of "emergency" in my book.

If you actually play this game you'll note that the laser isn't a neat pinpoint when it's shining at you.
Between scratches in the aircraft's window and the way your eye perceives light the laser pointer can completely blind the victim - check out the examples in the graphic below.
[

To date I don't believe any accidents have been attributed to laser illumination, but it is well within the realm of possibility, and the upward trend in laser illuminations of aircraft means the likelihood of such an accident is also increasing.
For more information check out the FAA's Laser Safety Initiative -- and particularly the video here.

and if a pilots eye is permanently damaged he may be unable to fly anymore

A 5 mW laser pointer even with minimal dispersion is highly unlikely to permanently blind a pilot beyond a few hundred feet, but unfortunately they sell ~500 mW lasers for <$100 nowadays...

An "accident" is (by definition) an event where aircraft is seriously damaged or anybody is injured. I believe there were some events where pilot had eye problems afterwards. Not sure if permanent, but if they can't continue their duty immediately afterwards, it is necessarily classified as injury (and therefore the event as accident).

@JanHudec I agree with you (as does the NTSB, though they qualify it as "seriously" injured), but in practice there is no NTSB or FAA document I'm aware of that I can point to saying "These are accidents where laser illumination was a causal or contributing factor" - as far as I know they're all classified as "incidents" right now.

@voretaq7: Quick search on The Aviation Herald shows 8 accidents where pilot was "injured" or "incapacitated", the most recent being Accident: Kelowna B722 at Regina on May 13th 2013, laser beam incapacitates first officer. Avherald uses the classification assigned by the investigating authority.

I would add that now there definitely is at least one accident in USA too.

@NickT Green lasers are a lot more dangerous at the same output level than red lasers, but you're right that 5 mW is not going to do permanent damage. But why is it unfortunate that people sell high-power lasers? They have legitimate uses.

Note that 5 mW is the top end of the range that can be legally classified as a "laser pointer".  The more typical (usually red) laser pointers that you buy to point at slides in a business meeting or annoy your cat are considerably less powerful.  Not that you should point even those at airplanes or other people, but it's not quite as bad.

Even if the laser doesn't cause temporary or permanent injury to the pilots' eyes, it causes them to lose night vision.
The most well-known cause of this is the pupils of your eyes.  In the dark, the pupils open up to allow in as much light as possible. When they're exposed to a sudden bright light, they close up again. If the bright light goes away, it takes your eyes some amount of time (say, a minute or two) for your pupils to open again. During that time, you can't see very well at all. Not good, if you're trying to land a plane. You can experience this for yourself by playing around with the lights indoors at night: if you turn the lights off, you can see very little but, gradually, you begin to make things out as your pupils open. If you then turn the light back on, it feels uncomfortably bright until you get used to it again.
Less well-known is a chemical called rhodopsin, in the rod cells in your retina. Rhodopsin is extremely sensitive to light (even to single photons), and light makes it change shape. Other proteins bind to this new shape and a few little chemical reactions result in an amplified signal being sent to your brain. Most of your vision in the dark comes from the rod cells because of their high sensitivity; the other cells (the cones) require tens to hundreds of photons to fire so they're great for colour vision in decent light but not much use in the dark.
However, being bound to other proteins means that the rhodopsin in your eyes is "used up" as light comes into your eyes. When its dark, this happens slowly enough that the rhodopsin can be regenerated but a sudden burst of bright light, such as from a laser, consumes all the rhodopsin in your eyes almost immediately.  Now, you're only seeing with the cones, and you're not seeing much. The really bad news is that it takes at least 5–10 minutes for a decent amount of rhodopsin to regenerate and 30–45 minutes to get back to the full amount. So now, your pilots are operating on quite seriously decreased vision for a substantial amount of time.

This is not true for red lasers, since rhodopsin is not particularly sensitive to red. That's why submarines will use red lighting at times, so if they have to surface in an emergency, their rods will not be saturated and they will not need to adjust.

@forest Do you have any data on that? Even though rods aren't very sensitive to red, we're still talking about a very intense red light here. Presumably red lasers aren't as bad, but that doesn't mean they're not a problem.

See https://en.wikipedia.org/wiki/File:CIE_1951_scotopic_luminosity_function.svg for the wavelength responses of various human photoreceptors. A red laser of 635nm would barely excite a rod cell, and 640nm would not affect it whatsoever. The amount of energy required to saturate a rod cell at 635nm would likely burn your retina. There's a little more information at https://en.wikipedia.org/wiki/Scotopic_vision and https://en.wikipedia.org/wiki/Luminosity_function as well.

@forest OK but egid's answer says that pilots have had their retinas burnt by lasers,

Those cases were all green lasers, which the eye is very sensitive to.

Retinal burning is just a matter of the intensity of the light. Your retinas can be burnt by UV, which they're not sensitive to at all.

That's true, but you were talking about loss of night vision. I was just pointing out that this would not be true for red lasers, which are very common. Of course a powerful enough light will burn your retinas at any wavelength, but at that point you're blinded due to photic retinopathy, not loss of night vision.

Some of the cheap, powerful lasers available now are capable of blinding pilots and in some cases causing lasting injury. Even temporary blindness, however, is something I think any pilot would consider an emergency.
A fairly recent Daily Mail article states that "the FBI noted that several commercial pilots earlier this year suffered significant injuries including a burnt retina." There are over 4000 reported incidents a year, and the number is apparently increasing rapidly. It is now a federal crime that has at least in one case resulted in prison time.

You can legally buy lasers that are certainly able to damage someone's eyes. They come with laser warnings for a reason, and being lasers, the intensity does not decrease much with distance. People with more powerful lasers could do even more damage.
This laser safety site has good info about the effects it has on the pilot and what can happen to you if you are caught doing this. Here is another article where the pilot suffered injury.
Laser illumination has not been identified as a factor in any accidents involving loss of life so far, but considering how many happen and the fact that they happen more and more often, it is certainly a hazard to safety and cause for declaring emergency.
Although many people charged with this crime claim their intentions were not malicious, that is certainly not always the case. Police helicopters are often targets, and this recent incident in Egypt is a notable example.

Now why buy, when you can make much, much more powerful lasers?

An incident where anybody is injured is classified as "accident", so in this sense they certainly were identified as cause of some.

@haneefmubarak I'd venture that most of the people who shine lasers on aircraft pilots aren't the kind capable of building their own laser :)

@Luaan that many people lack basic physics skills? Five minutes later... "Okay, so boys and girls, this is how you make a 5W laser..." XD

@haneefmubarak I think his point wasn't that so many people lack basic physics skills, but rather that so many people possess an understanding of right and wrong that includes potential outcomes here and excluding the few Dr. Evil's in our world, being capable of building your own laser likely puts you in the "smart enough to know not to do that" group.

@mah I suppose that makes sense...

@fooot I don't believe it is illegal (at least in the US) to possess a high power laser or that you needed a permit.

@fooot Perfect. After reading that, I was sweating bricks for a few minutes while I searched for laws about lasers :)


text:
Is there a real risk of ingesting FOD into jet engines when using thrust reversers?
In the discussion of Why doesn't the A380 use its outboard thrust reversers, one of the reasons given was that engines 1 and 4 would be at great risk of ingesting debris. It was pointed out that the 747 uses reversers on all 4 engines, and it's just as big (overhanging edge of runway). So I asked in a comment:

If there is fear that the outboard engines would ingest crap (FOD)
because they overhang the edge of the runway, why wouldn't that also
apply to takeoff, when the outboard engines are presumably at high
thrust? Additional: I realize that the jet blast is straight back, but suction on the front of the engine is pretty strong, too (enough to inhale a baggage cart).
Does an engine at reverse thrust kick air (and debris) far enough
forward that there is a real risk of ingestion and FOD?
Could that be negated by designing the reverse thrusters to go
mostly sideways?

I was asked to repost as a separate question, so here it is...

The A380 outboard engines are considerably further away from the centre line than those of the 747: https://upload.wikimedia.org/wikipedia/commons/5/52/Giant_planes_comparison.svg

For the numbered items:
(1) and (2) At takeoff there is (typically, but there are birds) nothing solid that's airborne in front of the airplane, whereas thrust reversers can put small but solid airborne material in front of the engines, especially if they're still being used with high power as the airplane slows.
(3) If you're saying that the air is only directed sideways rather that forward, that would cancel the forward thrust from that air, but it wouldn't get you much braking action.
Some other points:

The higher the airplane's speed, the more braking action you get from the reversers, so if you're going to use them, get into them as soon as possible.
If it's late night or early morning, and the airport has a noise problem, consider going into reverse but leaving the engines at idle. You'll still get significant braking proportional to the airplane's speed.
If you've got a long runway, consider using just idle or less than high-power reverse. In other words, use what you need/want, but no more.
Make sure you start out of a high power reverse well before slowing to taxi speed. There are speed guidelines for this, but I forget what they are. Actually, it's best in my opinion to avoid high-power reverse unless you really need it.
Make sure you're completely out of reverse by the time you reach taxi speed. Again, I've forgotten the guideline.
Consider where you are. If you're in, say, Germany, you can expect the runways to be clean, in Spain maybe not as clean, in Zimbabwe definitely not as clean. You get the idea.
Be really careful about using reverse on an icy runway. If your nose is not pointed straight down the runway, the reverse thrust will be working to put you off the side of the runway. An acquaintance of mine put a 747 off the runway at KJFK that way (totaled the airplane, a few people hurt, no fatalities).
Consider the characters of the engines on the airplane. Perhaps this is no longer a consideration, but back in the 1990s, P&W engines on the 747 were relatively tolerant of compressor stalls brought on by using too much reverse power at too slow a speed. GE engines, however, were not so tolerant.

The second 747 carrier I worked for used to have maintenance done at Santa Barbara, CA. When we would pick up the airplane, they would close the relatively narrow runway after our takeoff and sweep it. Not a reverse thrust situation, but it does illustrate the FOD problem.

the 747 runway departure, was it this?

When I say "sideways", I mean not deflected to 90 degrees, but simply not deflecting downwards, where it would send debris airborne. Maybe it's not feasible to build such asymmetric reversers? The old clamshell reversers could do it, but fanjets use a different mechanism.

Why would reverse thrust be dependent on forward speed (bullet 1)? Regarding your last bullet, I've heard of pilots trying to back out of the gate using reversers (no tug available), and they stalled or even damaged their engines.

@Frederico Yes. A friend of mine was in one of the jump seats and gave me a detailed account of the event as he recalled it.

@PhilPerry The way it was explained to me is that in reverse and at high speed, you have a lot of air with a relatively smooth flow coming in the front of the engine. As you slow, the amount of air the engine has to work with decreases, as well as increasing disruption to the smoothness of the flow. Also, the engine is having to do more "sucking." Explaining the physics of all that is beyond my expertise. In the case of the clam shell devices, it's also a matter of drag. Stick your hand out the window at 70 mph and it's harder to hold it there than at 20 mph.

@PhilPerry Using reverse thrust to backup (powering back) was done a lot with 727s. I seem to remember that AA did it regularly but then abandoned it because of problems. I backed up a 727 a few times. I never backed up a 747, but I knew a guy who did once. The big risk is FOD. The 727 engines are up high, the 747 down low and more susceptible. Compressor stall is a worry because of no forward speed pushing air into the engine; it's having to get it's air by sucking. Compressor stalls are never good for an engine, and severe stalls can ruin one. Maybe a question on compressor stalls?

On one flight, I can remember sitting at a window seat watching the engines as they were run up before brake release. There was a wonderful little "tornado" reaching from the lower lip of the intake cowl straight down to the ground. Re drag from clamshells, the additional drag during deployment might be a structural issue, but I would think the added braking effect would be welcome. Is there that much drag when undeployed?

the NTSB report @Federico shared in the above comment has been moved to http://www.ntsb.gov/investigations/AccidentReports/Reports/AAR9604.pdf


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Does it help to climb in case of a partial engine failure?
When the engines of a airplane show irregularities that do not reduce performance but indicate a possible failure of the engines, is it useful to climb to a higher level, to increase the glide length that is available in  case the engines stop completely?
The problem known in the cockpit is only that the engines do not run like they should. Say they make clearly unusual noises and slight vibration, but loose no performance. There is no indication whether the engines will fail, an in case the do fail, at which point in time that  will happen.
It's an emergency, without actual change in the planes performance.
As example, I think of a small single propeller plane, and a situation where longer glide path could be useful. But I think the question applies to any plane that can glide without power.

Sure it would, but the assumption is a situation where more glide path would be potentially helpful. Like when no airfield is reachable by gliding, but longer glide path allows more choice where to do the emergency landing.

Your assumption is that there is that the engine is good for another N minutes. It's hard to make such an assumption in the cockpit so I don't think a definite answer can be given. Climbing (and thus increasing engine speed) might strain your engine faster and in turn kill it even faster.

@Antzi It's not about n minutes, it's just "high risk to fail". I have edited to clarify. The engine speed is a good point.

Agreeing with @Antzi, high engine speed when combined with some sort of small scale physical damage or corrosion is a typical failure mode for propeller engines. Combining that logic with the fact that propeller engines run more efficiently at lower elevations (higher air density) I would recommend against climbing. In fact, lowering your elevation and speed will greatly reduce the stress/strain you are putting on the engine and will likely give you a better chance of making it safely to the closest airfield.

I recently saw a YouTube Video with this exact scenario in a single prop Cirrus plane.  He did not climb but rather turned back to the airport and maintained a higher altitude than normal for the approach for landing.  ATC was giving him clearance to descend for the landing but he rejected that clearance in order to give him some altitude in case his engine did fail.

Okay, as I understand your problem you have an engine that is suspect to possible failure. So, you are asking, if it is a good idea to increase the stresses on the engine to climb by adding more power and possibly increase the chances of a potential failure. Unless you are looking at an immediate confrontation with a object on the horizon that is higher than your current altitude, like a big rock, I would reduce power to a minimum and look for a place to land. If you are in a four engine jet at, let's say FL 390, the last thing you would consider is climbing because, if you loose an engine at that altitude, decent will be mandatory immediately because three engines will not sustain flight at that altitude.


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What is a grid course?
Reviewing the ILS 7 approach at Barrow (PABR) revealed something I have never seen before:

Now, I saw the note (and diagram) in the upper left corner, so I was able to infer that this is a "grid course" but I still have no idea what this is.
Is there anyone on Aviation SE that knows and can explain?

This website explains.


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Why did Air France retire Concorde?
It was developed by British Airways and Air France in the 1970s as the first supersonic passenger/civilian airplane.

possible duplicate of: http://aviation.stackexchange.com/questions/3782/what-are-the-barriers-to-feasibility-of-stratospheric-cruising-for-commercial-ai

This is already covered in detail on Wikipedia. What are you looking for that isn't already written there?

Concorde wasn't developed by British Airways and Air France. Although the airlines ended up being the sole operators, the aircraft was developed and built by a consortium of aircraft manufacturers. Initially Bristol and SUD later Aerospatiale/BAC.

There has been a very interesting program on the french public service radio France Inter just this week on this exact matter.

This question appears to be off-topic because it is about Trivial Facts easily determined in Wikipedia.

Ultimately the cost of flying the aircraft was more than the revenue that it generated.  The Concorde began a steady decline to retirement after the firey crash of Air France Flight 4590 which killed 113 people, and again suffered setback after September 11th, 2001.  Even with the best safety record in airline history, the crash combined with the terrorist attacks led to passenger fear and low sales. Airlines that operated the Concorde eventually lost money on most flights, and long term operations were simply not sustainable.  To make matters worse, it was very limited to which airports it could fly to in the US: JFK, IAD and DFW. The FAA was opposed to the Concorde for pollution, noise and fuel inefficiency concerns.
British Airways cites mostly political reasons for the ending of its Concorde program.  They claim that the Concorde would have remained profitable had Airbus retained the airplane.  However, there was also speculation that, due to the dwindling numbers of passengers, BA realized that it could make more money carrying passengers subsonically across the Atlantic.

@SHAF and that it wasn't US made.

Flights were limited to those airports in the US... there are lots of other airports in the world! Concorde did fly to several other destinations, but it also met with problems overflying some countries and the fact it wasn't allowed to go supersonic over land (limiting it's use for many routes). It was only ever really viable for Transatlantic flights from Western Europe to the Eastern US and Caribbean.

Note also that Concorde WAS profitable when used by BA later in it's service life... BA realised that people thought the cost for a ticket was higher than it actually was, and simply increased the price to match. BA's usage was eventually shut down by the manufacturer ending maintenance support.

@JonStory Updated to reflect suggestion

Regarding "the best safety record in airline history," didn't it pretty much go from the best to one of the worst after AF4590? When you only have 14 aircraft in airline service, one fatal accident changes your statistics dramatically. Of course, it seems a bit unfair really to have even called it the most safe in the first place, since it never had enough flight hours for a statistically meaningful comparison with other airliners. Even with the 737 and A320 series, one accident is enough to dramatically change the statistics.

Why did Air France retire the Concorde
It wasn't making money - in fact, it was losing money. Huge fuel price increases shortly after it was brought in meant it was never really profitable for Air France. Then double-whammy of the Air France Flight 4590, followed a few years later by 9/11 hitting Airlines hard in reduced passenger numbers (particularly into New York), caused Air France to consider it no longer viable to run even as a loss-making flagship service.
Why did British Airways retire the Concorde
A related but separate question, BA actually found a way to make their Concorde's profitable later on. They discovered that the public (particularly the business users who weren't paying for their own tickets...) thought Concorde tickets were more expensive than they actually were, so merely increased the price to match. They were profitable for several years until Airbus announced they were no longer going to maintain or support the aircraft.

The Concorde did fly for several years, but it couldn't fly supersonic over land (as Steve pointed out, it was able, but not allowed due to concerns about the sound of the sonic boom) and it guzzled fuel. In the end, it wasn't economically viable.

Was not permitted to fly supersonic over land.

"Concorde did fly for several years" 27 is about two decades more than "several". And it had been forbidden from flying supersonic over land for the whole of that time, so why did the inability to go supersonic over land suddenly cause Concorde to be retired in 2003, rather than in 1983?